Influence of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) in comparison to dicyandiamide (DCD) on nitrous oxide emissions, carbon dioxide fluxes and methane oxidation during 3 years of repeated application in field experiments

Abstract.

In a 3-year field experiment, the effect of the nitrification inhibitor (NI) 3,4-dimethylpyrazole phosphate (DMPP) on the release of N₂O, CO₂, and on CH₄ oxidation, was examined in comparison to that of dicyandiamide (DCD) on N-fertilized and unfertilized experimental sites. Soil samples were analysed simultaneously for the concentrations of N₂O retained in the soil body, NH₄ ⁺, NO₂ ^–, NO₃ ^–, and for the degradation kinetics of DMPP as well as DCD. DMPP decreased the release of N₂O on fertilized plots by 41% (1997), 47% (1998) and 53% (1999) (on average by 49%) while DCD reduced N₂O emissions by 30% (1997), 22% (1998) and 29% (1999) (on average by 26%). In addition, the NIs seemed to decrease the CO₂ emissions of each fertilized treatment. DCD reduced the release of CO₂ by an average of 7% for the 3 years (non-fertilized 10%), and DMPP reduced it by an average of up to 28% (non-fertilized 29%). Furthermore, both NIs failed to affect CH₄ oxidation negatively. The plots that received either DCD or DMPP even seemed to function as enhanced sinks for atmospheric CH₄. DMPP apparently stimulated CH₄ oxidation of N-fertilized plots by ca 28% in comparison to the control. In total, DCD and DMPP reduced the global warming potential of N-fertilized plots by 7% and 30%, respectively. Further, DCD and DMPP diminished the amount of N₂O retained in the soil by 52% and 61%, respectively. The concentrations of NH₄ ⁺ remained unaffected by both NIs, whereas the amounts of NO₂ ^– diminished in the plots treated with DCD by 25% and with DMPP by 20%. In both NI treatments NO₃ ^– concentrations in the soil were 23% lower than in the control. DMPP and DCD did not affect the yields of summer barley, maize and winter wheat significantly. DCD was mineralized more rapidly than DMPP.